The present invention relates to electrical systems and, more particularly, to electrical systems for reducing power consumption by electrical appliances. A major objective of the present invention is to reduce the power consumption of an appliance by withholding power over time periods selected to minimize interference with the usefulness of the appliance.
Despite an increasing awareness of the importance of energy conservation, the demand for electrical power has been increasing; this increase is due, in large part, to the increasing prevalence of computers and power-hungry peripherals such as laser printers. In many cases, the appliances collectively draw more power than the building in which they are housed was designed to manage. Options such as rewiring a building and moving into another building are expensive. Thus, both economic and conservation considerations place a premium on limiting power consumption.
Many appliances are now designed to minimize power consumption. In part, this is accomplished by including intelligent power management capabilities. For example, many devices turn off or enter a very-low-power sleep mode after a certain lapse of time without use. However, many legacy appliances and even some recently available appliances do not employ effective power management.
Moreover, many devices that do incorporate power management do not do so optimally. For example, many devices power down after a predetermined period of non-use. In many cases, appliances that shut down during business hours or when a potential user is in the vicinity incur a cost, whether in lost revenues or in productivity, e.g., in the case of a copy machine that forces users to wait while it warms up.
Appliances with less-than-optimal power management call for add-on devices that reduce power consumption by turning off power to the appliance during periods of nonuse. A typical external power-management device is designed to be plugged into a wall outlet and includes its own outlet into which the appliance is plugged. A switch internal to the power-management device determines whether or not the appliance is coupled electrically to the wall outlet.
Such external power management faces challenges beyond those faced by internal power management. Appliances are designed to detect certain inputs and to initiate certain actions; thus, the appliances are "informed" when the inputs and actions occur. However, such appliances do not, in general, make such information available to external devices. Also, in general, such information is not easily accessed or duplicated by external devices. Thus, it can be difficult to design an external power-management device that determines shutdown based on usage and internal activity as effectively as an appliance designed from the outset to address power management.
Some external power-management devices incorporate occupancy detectors to address the lack of direct usage data. An appliance is more likely to be being used or to be about to be used if there is a person in its vicinity. Occupancy is relatively useful for determining when to power on an appliance. For example, security lights often use occupancy sensing (motion detection); lights are turned on when motion is sensed. Typically, security lights are turned off after a predetermined elapsed time during which no motion is detected. Occupancy sensing can be coupled with other forms of sensing; for example, security lights often monitor ambient light and preclude activating the lights when the ambient light is ample.
Occupancy is not as useful when it comes to determining a shutdown time for appliances that can be remotely activated (e.g., a networked printer) and for appliances that undergo self-initiated procedures (e.g., a vending machine compression cycle) that should not be interrupted. While information about remote activation and internal cycling is available to the appliance, it is not, in general, available to an external power-management device. What is needed is an external power-management device that provides a better tradeoff between power conservation and convenience.